Automated identification of chest radiographs with referable abnormality with deep learning: need for recalibration

Abstract

Objectives To evaluate the calibration of a deep learning (DL) model in a diagnostic cohort and to improve model's calibration through recalibration procedures. Methods Chest radiographs (CRs) from 1135 consecutive patients (M:F = 582:553; mean age, 52.6 years) who visited our emergency department were included. A commercialized DL model was utilized to identify abnormal CRs, with a continuous probability score for each CR. After evaluation of the model calibration, eight different methods were used to recalibrate the original model based on the probability score. The original model outputs were recalibrated using 681 randomly sampled CRs and validated using the remaining 454 CRs. The Brier score for overall performance, average and maximum calibration error, absolute Spiegelhalter'sZfor calibration, and area under the receiver operating characteristic curve (AUROC) for discrimination were evaluated in 1000-times repeated, randomly split datasets. Results The original model tended to overestimate the likelihood for the presence of abnormalities, exhibiting average and maximum calibration error of 0.069 and 0.179, respectively; an absolute Spiegelhalter'sZvalue of 2.349; and an AUROC of 0.949. After recalibration, significant improvements in the average (range, 0.015-0.036) and maximum (range, 0.057-0.172) calibration errors were observed in eight and five methods, respectively. Significant improvement in absolute Spiegelhalter'sZ(range, 0.809-4.439) was observed in only one method (the recalibration constant). Discriminations were preserved in six methods (AUROC, 0.909-0.949). Conclusion The calibration of DL algorithm can be augmented through simple recalibration procedures. Improved calibration may enhance the interpretability and credibility of the model for users.